Railroads maintain a vital position in the transportation of goods and, to a lesser extent, passengers. The maintenance of the current rail system and the establishment of new rail line requires a continuous source of new railroad rails.
Traditionally, rails have been manufactured in lengths of about 39 feet by reverse rolling rectangular blooms. While it is known that blooms can be produced for a variety of steel shapes in virtually any desired cross-section, the cross-section of blooms from which rails are rolled has traditionally been rectangular. This is principally due to the fact that a finished rail has a cross-section which loosely approximates a rectangle, in that it has a flat base, a roughly vertical web and a more or less flat head, although of course the web is much thinner than the base or head. Therefore, the rail can be produced from a rectangular bloom with less rolling than from, for example, a circular bloom. From the standpoint of rolling efficiency alone, without considering other factors, it is generally thought that it is better to start with a rectangular bloom than with a square bloom. In addition, rectangular blooms are easier to stack and handle than circular blooms.
These advantages of a rectangular bloom over a circular bloom in the production of rails is believed to be offset by other factors. One set of factors relates to the casting process and another set of factors relates to the quality of the finished rail. A continuous caster of the type used to produce large blooms for rolling large shapes such as rails is easier and less expensive to manufacture and maintain if the blooms are round rather than rectangular. Moreover, the number of continuous caster strands may be reduced because a round bloom can be produced at a higher rate than a rectangular bloom and the strand design can be simpler. See, e.g., Ing, Pleschiutschnigg, Rensch, Obering, Schrewe, Continuously Cast Rounds in Combination with the High Reduction Technology to Produce Rods, Bars and Sections up to Medium Size Range, Fachberichte Huttenpraxis Metalweiterverarbeitung, Vol. 25, No. 4 1987.
Regarding the quality of the finished rail, a round bloom cools much more uniformly than a rectangular bloom since the round bloom has no undercooled edges. This results in an improved product that is metallurgically more uniform with a better surface quality.
The 39 foot length of traditional rails was due to the length of the railroad cars that carried the rails to the installation site. At the installation site, the 39 foot sections were bolted together to form a continuous rail. The resulting continuous rail had joints every 39 feet which produced a bumpy ride and were susceptible to wear. Later methods utilized somewhat longer rail lengths such as 100 feet in order to lessen the number of joints in the installed rail, or attached the individual rail lengths to one another by welding rather than by bolting to produce a smoother and better wearing joint. Even then, however, there was a noticeable joint that produced a bumpy ride and was susceptible to wear. Still later methods performed the majority of the welds at the rail manufacturing facility to produce very long sections comprising a number of welded together smaller sections. The long sections were then transported to the installation site and joined there. The result was a rail having high-grade closely-spaced welds made at the manufacturing facility together with lower-grade longer-spaced welds made at the installation site. While this rail is an improvement over previous methods, even the high-grade welds made at the manufacturing facility resulted in a noticeable joint that produced a bumpy ride and lead to wear. A vast improvement over these prior art methods was finally described in U.S. Pat. Nos. 5,018,666 and 5,195,573, assigned to the assignee of the present invention. Those patents describe a very long rail, such as 200 to 500 feet to a quarter mile, that is produced seamlessly by a continuous rolling process. When installed, that rail includes long-spaced welds made at the installation site as in the case of conventional rails, but does not include any closely-spaced welds or other joints. The installed rail is thus less expensive to manufacture, results in a smoother ride, and is better wearing. The long rail and rolling process of the above-referenced patents may be used in the process of rolling rails from circular blooms as described in the present patent.